X-ray cassettes are disclosed in, for example, Published Examined Japanese Utility Model Application No. 55-50672 and Published Examined Japanese Patent Application No. 58-33540 (German Utility Model Application No. 812806). The former X-ray cassette has a metal frame provided around a front plate. The latter X-ray cassette has its front plate and frame made integrally of plastic, and has flexible members attached to the corner portions of the frame to absorb shocks caused by falling or the like, thereby preventing the X-ray cassette from being damaged.
The frame of the former X-ray cassette is formed by cutting an elongated metal member, such as an aluminum extruded member or roll-molded member, to the proper length, bending the cut member to match the shape of the front plate, and joining its but-joint ends together by means of welding or the like. Although the X-ray cassette is excellent in term of the durability, shock resistance, etc. due the frame being made of metal makes the manufacturing thereof troublesome. In other words, the cross-sectional shape of the frame should be determined in consideration of the bending formation, which limits the improvement thereof in terms of strength. Further, deformation or twisting may occur at the time of bending the metal member. Furthermore, there may be a slight error in the bent positions of the frame; particularly, insufficient strength, the occurrence of deformation, twisting or the like, and an error in the bent positions should be considered for a large cassette for retaining a broader film.
Since the latter X-ray cassette is made of plastic, it is easy to produce and is excellent in terms of obtaining accuracy in sizes. Because of the plastic-formed, however, the X-ray cassette has low durability and low shock resistance, making it easy to cause deformation with the passage of time.
It is therefore an object of the present invention to provide an X-ray cassette which has an improved strength, is free of deformation, twisting or the like, is easy to manufacture, and can improve the size accuracy.